Sanitary napkin with cross-linked cellulosic layer



Sept. 5, 1967 c. c. VAN HAAFTEN SANITARY NAPKIN WITH CROSS-LINKEDCELLULOSIC LAYER 2 Sheets-Sheet Filed April C", 1964 2 Sheets-Sheet 2wmw;

C. C. VAN HAAFTEN SANITARY NAPKIN WITH CROS S LINKED CELLULOS I C LAYERinw nnUAVAVnVAVAVAAVAVA'J :.v 1l/:SAV nv nt Av nv "a am Sept. 5, 1967United States Patent O of Delaware Filed Apr. 7, 1964, Ser. No. 357,9468 Claims. (Cl. 12S- 290) The present invention relates to disposableabsorbent pads such as sanitary napkins, diapers, hospital pads and thelike. More particularly, this invention relates to improvements in theconstruction of absorbent pads to provide more effective control of theflow of body fluids which strike the pad and are absorbed therein.

In absorbent pads, and especially sanitary napkins, it is highlydesirable that the construction be such that any discharged body fluidswhich strike the surface thereof be carried to the interior of the padas rapidly as possible to be distributed evenly throughout the interiorabsorbent portion and retained therein. If this is accomplishedeffectively, excessive spreading of the fluid on the pad surface isavoided with the result that undesirable surface staining is minimized,while the pad area which contacts the body remains substantially dry,thus promoting a sense of comfort and security `for the user. While mostsanitary napkins now on the market function satisfactorily in mostrespects, the problem of preventing excessive surface staining has notbeen successfully solved. One of the most common complaints receivedfrom users by manufacturers of sanitary napkins relates to soiledunderclothing largely attributed to such staining. Apparently, if thebody fluid has spread over the pad surface because of slow absorption int-he pad, or as the result of heavy flow, it also spreads to theclothing; if the fluid 'spread on I the pad surface is minimal, theclothing is not affected.

Accordingly, it is a major object of this invention to provide anabsorbent pad in which the spreading of fluids on the surface isminimized.

Another object is to provide sanitary napkins with a component whichacts as an effective fluid transfer element to rapidly wick acceptedbody fluids away from the napkin surface to the interior of the napkinwhere it is evenly distributed and absorbed.

A further object is to provide a sanitary napkin in which fluid absorbedin the interior thereof is substantially prevented from mig-rating backto the exterior.

Other objects and advantages will become apparent from the followingdescription and appended drawings, inwhich:

FIG. 1 is a perspective view of an absorbent bandage of the presentinvention taken from the bottom side, with a section of the pad cut awayand the wrapper partially open.

FIG. 2 is a sectional view of the bandage shown in FIG. 1, but with thetop and bottom in the normal positions as worn.

FIG. 3 is a View similar to FIG. 2 of an alternate construction.

FIG. 4 is a sectional view of another construction.

FIG. 5 is a sectional view of still another possible construction.

The above objects are attained by constructing an absorbent bandage in amanner to include a highly resilient fluffy layer or batt of speciallymodified fibers in close proximity to the usual pervious outer wrapper,with an internally disposed highly absorbent element in contiguousassociation therewith. The modified fibers which make up the resilientlayer are internally cross-linked cellulosic fibers of a typehereinafter described. In one embodiment, the layer of cross-linkedfibers is located only on the body side of the bandage overlying anabsorbent core. In this position, the cross-linked fiber layer acts asan effective fluid transfer agent to rapidly wick accepted fluid downinto juxtaposed layers on the interior of the bandage where it isabsorbed, distributed, and held by underlying components.

In another embodiment, the layer of cross-linked fibers may extendaround each side, and in contiguous association with an absorbent core.In this construction, that portion of the layer which lies on the top ofthe core acts in the same Way as described above. That portion whichlies on either side of the core inhibits the fluid which has beenabsorbed in the interior from migrating outward, thus also preventingside stains. The resilient nature of the cross-linked fiber layer alsoadds to comfort by remaining dry and airy while providing additionalcushioning.

In still another embodiment, the layer of cross-linked fibers maycompletely enclose an absorbent core. In this construction, the bandagemay be worn with either` side up. Fluid will strike through aspreviously described, but will 'be effectively trapped in the absorbentcore within the layer, if the absorbent core is not super-saturated,which sometimes happens inadvertently when the bandage is worn too long.

As shown in the drawings, absorbent bandages, such as sanitary napkins,generally comprise an absorbent pad 10 wrapped in a pervious outerwrapper 11. In the embodiment shown in FIGS. 1 and 2, the pad 10comprises a fluid flow control element 12 comprising an assembly ofcross-linked cellulose fibers, a multiple layer of absorbent cellulosewadding 13, a layer of absorbent cellulosic fluff 14 wrapped in anoptional sheath of creped wadding 16, and a fluid impervious baille 15,which may consist of thin plastic such as polyethylene or the like. Theentire combination is held in unitary assembly by an outer perviouscovering 11 which may comprising gauze, non-woven threads, non-wovenfabric, or the like.

In an alternate embodiment, shown in FIG. 3, the pad assembly comprisesthe cross-linked fiber element 12, a layer of absorbent fluff 14 wrappedin an optional sheet of creped wadding 16 and a fluid impervious baffle15.

In other embodiments, as shown in FIGS. 4 and 5, the element 12comprising'cross-linked fibers may extend from the top of the absorbentcore down along each side thereof (FIG. 4) or even completely around thecore (FIG. 5).

Other suitable assemblies of absorbent elements may also be used.However, in each case, it is necessary that the element locatedimmediately under the top or body side of the wrapper comprisecross-linked cellulose fibers as identified by the number 12 in thedrawing. For various mechanical or functional reasons, very thinfluid-pervious sheets or apertured material may be interposed betweenthe cross-linked element and the wrapper, butin any event, suchmaterials should be of a type which do not inhibit fluid transfer fromthe surface of the pad to the interior.

The cross-linked cellulosic fibers which comprise element 12 areassembled in the form of a loose fluffy mass. Such a mass has a lowresistance to fluid flow, yet exhibits a high capacity for fluidretention in interstitial spaces between fibers, without materialphysical distortion of the fiber mass, even in a wetted condition. Theexterior of the fibers is easily wetted as the fluid is drawn into theelement, but virtually no interior absorption or swelling occurs withinthe individual fibers. It has been found that an element comprising aloose, fluffy mass of the crosslinked fibers tends to give up fluidsnormally retained therein to a contiguously associated, more compact,absorbent fibrous element having finer capillary spaces between fibers.

The cross-linked fibers employed in this invention are characterized byan internal cross-linking, particularly ether linkages between moleculesof the cellulose. Such fibers are obtained by first impregnatingcellulose in fiber form with an aqueous solution containing across-linking agent and a catalyst. The moist mass of fibers is thenexpanded into a loose, fluffy condition and while in such loosecondition is dried Without effecting substantial crosslinking. The driedfluffy mass is then subjected to an increased temperature which issufficiently high to cause a cross-linking reaction to take place whilemaintaining the mass in its loose, fluffy condition. The reacted fibersare subsequently washed, to remove unreacted constituents, and dried.

The particulars of the cross-linking treatment are set forth in detailin copending application Serial No. 204,528 filed June 22, 1962, whichissued Dec. 2l, 1965, as Patent No. 3,224,926. As described in thatapplicaton, the cellulosic fibers which may be used include any of theWood pulp fibers used in papermaking, hemp fibers, short cotton fibers,alpha cellulose, cotton linters, short-cut regenerated cellulose fibers,and the like. Wood pulp fibers are generally preferred. The preferredcross-linking agents are formaldehyde or dimethylol urea, but otherknown cross-linking agents and suitable catalysts may be used. Aparticularly effective catalyst is aluminum sulfate. The impregnation iseffected while the fibers are expanded or swollen, thus insuring entryof the cross-linking agent and catalyst in quantity to the fiberinterior. After impregnation, the fibers are dried and collapsed inwhich condition the cross-linking reaction is carried out.

The temperature for the cross-linking reaction is dependent to someextent upon the nature of the cellulosic fiber used; for Wood pulpfibers the preferred range is between 110-l65 C. The resulting fibersretain the natural shape of the original fibers, but in their modifiedstate are more rigid, even when wetted, and are less deformable underload, thus providing improved dimensional stability. The rigidity of themodified fibers, while not such as to render the fiber mass brittle, issuch that the fibers will reduce to a powdered state rather thanplasticize or hydrate when subjected to a refining or beating action, asusually employed in the papermaking art. For use as the flow controlelement of this invention, it is important that the cross-linked fibersbe retained in their fibrous state rather than being broken up byrefining or beating.

The cross-linked cellulosic material, while in t-he fibrous conditiondescribed above, is assembled in a loose batt or fluff form, and in thisform exhibits an unusually high wet stiffness, high wet -bulk andporosity, high wet resiliency, low dry density, and low wetconipressibility, as compared to the same properties in a batt ofnon-crosslinked cellulose fibers. These batts also have a high wickingrate for aqueous and other polar fluids. By a high wicking rate it ismeant that such fluids are transported rapidly through the batt bycapillary forces.

It has been found that fibers cross-linked as above described havegreater bulk and about twice the resistance to compression in the wetstate as untreated pulps and at least 50% greater recovery after suchcompression. It is these properties, and the concomitant high wickingrate, which apparently provide the absorbent bandages of this inventionwith their unique advantages with respect to minimizing surface stains,when suitably combined with other more conventional absorbent elements.

The rate of wicking of fluids through fibrous batts made fromcross-linked material as above described may be demonstrated in variousways. In one example, a flat transparent plate approximately 3 x 3 wasused to hold a 21/2 x 41/2 batt. The batt projected beyond one edge ofthe plate for approximately 11/2" into an aqueous dye solutionmaintained at a constant level. The time for the dye to wick completelythrough the batt to its opposite end was measured. For a fiber batt ofcross-linked Wood pulp fibers, wicking time was 20 seconds. Foruntreated fibers from the same source, wicking time was 49 seconds.Thus, the MOSS-,linked fiber batt had a wicking rate ap- 4 proximately21/2 times faster than a batt yof untreated fibers.

The cross-linked fibers have been found to work most effectively in theform of a fluffy, loosely assembled component located immediately belowthe bandage wrapper on the side of the bandage which is in contact withthe body. In this position, the cross-linked fluff cornponent functionsas an effective fluid transfer agent to rapidly wick the fluid down intocontiguous interiorly disposed absorbent elements to be evenlydistributed therein. With the rapid wicking properties of the assembledfibers, one would normally expect the accepted fluids to spreadtransversely in the element as well. However, under the definedconditions, there is virtually no horizontal -or transverse migration offluid within the cross-linked fiber element when positioned contiguousto conventional absorbent material. This unexpected result effectivelyreduces the area of top stains, and is especially advantageous forsanitary napkins. The surface thus is maintained relatively dry and thenapkin is more comfortable in use.

Resistance to side stains is also increased when the cross-linked fiberelement is made wide enough to extend down from the surface area alongeach side of the absorbent inner elements. It has been found that, forsome reason, the fluid which has been absorbed in the inner element doesnot migrate outwardly through the cross-linked fibers positioned alongthe sides With the result that side stains are also minimized.

It has been found furt-her, that when the absorbent inner element iscompletely enwrapped by a cross-linked fiber element, fluids areeffectively trapped within the inner element and will not migrateoutwardly in any direction through the cross-linked fiber element.

The reason for this latter phenomenon, in view of the recognized rapidwicking properties of the cross-linked element, is not entirelyunderstood. It is believed at tributable to the fact that because theinterstitial pore size `of the absorbent inner elements is much smallerthan the pore size of the cross-linked fiber element, the inner elementhas a stronger capillary attraction for the absorbed fluids. Theinterstitial pore size of the cross-linked element is relatively largeand since the pore size is not reduced, even under wet compression, thefluids apparently tend to remain in the central element having thesmaller pore size.

As noted above, in order for the cross-linked element to Work mosteffectively, it is essential that the element be located in closeproximity to the fluid pervious bandage wrapper, and between saidwrapper and a contiguously placed lower or central absorbent material.Any type of conventionally used absorbentl material, such as cellulosewadding, cotton fiber batts, wood fiber fluff and the like, may beemployed as the inner absorbent elements of the pad. In the embodimentss-hown in FIGS. l and 2, the other absorbent elements comprise multiplelayers of cellulose wadding lover a layer of wood fiber fluff and abottom impervious baffle. In FIGS. 3, 4, and 5, the absorbent layerconsists entirely of word fiber fluff. Various other combinations andarrangements of baffles and ab` sorbent elements may also be used.

The amount of cross-linked fiber material used is not too critical, butshould be adjusted in accordance with the flow rate expected. In a padweighing a total of from about l0 to 14 grams, cross-linked fiber battsweighing from 0.5 to 4.0 grams per 16 square inches have been used. Ineach instance, surface stains were reduced when compared with pads whichhad no cross-linked element present. The thickness of the cross-linkedelement is preferably suflicient to at least partially mask the darkcolor of the -body fluid absorbed in the interior of the pad. For suchpurposes, a thickness `of JAG" has been found satisfactory. Forsuper-size pads, which are designed for women with extra heavy flow,much thicker cross-linked elements may be employed.

While the preferred embodiments of the invention have been shown anddescribed herein, it will be appreciated that the details may be more orless modified without departing from the principles and scope of theinvention as defined in the appended claims.

What is claimed is:

1. An absorbent bandage comprising a fiuid absorbent pad, a fluidpervious outer wrapper, and, between the iiuid absorbent pad and theouter wrapper, a layer of bers in mass form, said iibrous masscomprising a loose assembly of cross-linked cellulosic bers, said fibersbeing cross-linked while in the collapsed dry state to a degree whereinsaid fibers are not readily plasticized by contact with aqueous iiuids,said iibrous mass being characterized by a larger pore size than thepore size of said absorbent pad and a capacity to rapidly wick iiuidstherethrough into contact with, and absorption by, said absorbent pad.

2. The absorbent bandage of claim 1 in which the cross-linked fibers arewood pulp fibers.

3. In an absorbent bandage comprising multiple layers of absorbentmaterial enwrapped in a iiuid pervious Wrapper, the improvement whichcomprises providing a battlike layer of loosely assembled, cross-linkedcellulose fibers between and in contiguous association with saidabsorbent material and said wrapper, said cross-linked while in thecollapsed dry state ibers being cross-linked to a degree where they arenot readily plasticized by contact with aqueous fluids, said layer ofcross-linked iibers having a larger pore size than the pore size of saidlayers of absorbent material.

4. A sanitary napkin with improved resistance to top staining whichcomprises superposed layers of fluff-like cellulosic material enwrappedin a fluid pervious wrapper, the top layer of said material comprising abatt of loosely assembled, cross-linked cellulosic iibers, said fibersbeing cross-linked while in the collapsed dry state to a degree wherethey are not readily plasticized when contacted with aqueous iiuids, theremaining layers of said material comprising loosely assembled woodfluff having a smaller pore size than the pore size of the cross-linkedfiber batt.

5. A sanitary napkin comprising an elongate fluid receptive pad and auid permeable wrapper, said pad comprising multiple continuous layers ofbrous material, said multiple layers comprising a first layer of looselyassembled, cross-linked fibers in which the fibers are cross- `linkedwhile in the collapsed dry state to a degree where said fibers are notreadily plasticized when contacted with aqueous fluids, a second layerof absorbent cellulose wadding sheets, a third layer of looselyassembled wood fiber fluff, and a bottom iiuid impervious layer, saidlayer of cellulose wadding sheets and said layer of wood fiber fluffhaving a smaller pore size than the pore size of the layer ofcross-linked iibers.

6. A sanitary napkin comprising an elongate absorbent pad and a fluidpermeable wrapper, said pad comprising multiple layers of cellulosicmaterial including a rst layer of cross-linked cellulosic fibers whereinthe cross-linking has been carried out while said fibers are in thecollapsed dry state to a degree wherein said bers are not readilyplasticized when contacted with aqueous fluids, a second layer ofcellulose uf, and a bottom fluid impervious layer, said fluff layerhaving a smaller pore size than the pore size of the layer ofcross-linked yfibers.

7. A sanitary napkin according to claim 6 in which the cross-linkedlayer extends down along either side of said second layer.

8. A sanitary napkin comprising an absorbent pad and a fluid permeablewrapper, said pad comprising a central absorbent core of untreatedcellulosic material completely encircled by a layer of cross-linkedcellulosic bers, said fibers being cross-linked while in the collapseddry state to a degree wherein said fibers are not readily plasticizedwhen contacted with aqueous fluids, said cross-linked iber layer havinga larger pore size than the pore size of said adsorbent core ofuntreated cellulosic material.

References Cited UNITED STATES PATENTS 2,896,627 7/1959 Harwood 128--2903,017,304 1/1962 Burgeni 12S- 290 X 3,029,817 4/ 1962 Harwood et al128--290 3,046,986 7/ 1962 Harwood 12S-290* 3,055,369 9/1962 Graham128-285 3,241,553 3/ 1966 Steiger 128-290 X RICHARD A. GAUDET, PrimaryExaminer. CHARLES F. ROSENBAUM, Examiner.

1. AN ABSORBENT BANDAGE COMPRISING A FLUID ASORBENT PAD, A FLUIDPERVIOUS OUTER WRAPPER, AND, BETWEEN THE FLUID ABSORBENT PAD AND THEOUTER WRAPPER, A LAYER OF FIBERS IN MASS FORM, SAID FIBROUS MASSCOMPRISING A LOOSE ASSEMBLY OF CROSS-LIKED CELLULOSIC FIBERS, SAIDFIBERS BEING CROSS-LINKED WHILE IN THE COLLAPSED DRY STATE TO A DEGREEWHEREIN SAID FIBERS ARE NOT READILY PLASTICIZED BY CONTACT